1. Field
This invention is directed generally to turbine blades, and more particularly to a shrouded turbine blade.
2. Description of the Related Art
Typically, gas turbine engines include a compressor for compressing air, a combustor for mixing the compressed air with fuel and igniting the mixture, and a turbine blade assembly for producing power. Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures.
A turbine blade is formed from a root portion at one end and an elongated portion forming an airfoil that extends outwardly from a platform coupled to the root portion. The blade is ordinarily composed of a tip opposite the root section, a leading edge, and a trailing edge. The tip of a turbine blade often has a tip feature to reduce the size of the gap between ring segments and blades in the gas path of the turbine to prevent tip flow leakage, which reduces the amount of torque generated by the turbine blades. Some turbine blades include tip shrouds, as shown in FIG. 1A, attached to the blade tips.
Tip leakage loss, as shown in FIG. 1B, is essentially lost opportunity for work extraction and also contributes towards aerodynamic secondary loss. To reduce over-tip leakage, shrouded blades typically include a circumferential knife edge for running tight tip gaps. The turbine tip shrouds are also used for the purpose of blade damping.
A tip shroud increases the weight at the blade tip and contributes to extra loadings to the blade lower section, caused by centrifugal forces resulting from the weight of the shroud. Some modern tip shrouds are scalloped, as opposed to a full ring, to reduce shroud weight and hence lower blade centrifugal pull loads, with mechanical support being provided through the knife edge seal. The material removed by scalloping is indicated by the shaded region in FIG. 1A. The removal of material by scalloping is detrimental to turbine aerodynamic efficiency, as the shroud coverage is now reduced leading to an increase in parasitic leakage.